1. Field of the Invention
The present invention relates to a pigment/auxiliary combination having an improved chrome and/or relative colour strength, to its production and to its use.
Inorganic pigments are encountered in numerous areas of everyday life. They are used for colouring building materials such as concrete and asphalt, emulsion paints, other coating materials, plastics, and so on. Very often, however, the pigments are additionally coated subsequently, after the actual synthesis. The purpose of such coating is essentially to achieve further improvement in the qualities of the pigments.
2. Brief Description of the Prior Art
EP 0 199 975 A1 describes red iron oxide pigments having improved colouristic qualities, the isoelectric point of the pigments being greater than 7, with particular preference greater than 8. The pigments described in accordance with this teaching are required to have a coating, which is composed of colourless compounds of one or more elements from the group Mg, Zn, Al, La, Y, Zr, Sn, or Ca. Compounds suitable for the coating are low-solubility compounds of Mg, Ca, Al and/or Zn, and are applied to the pigment by spraying, painting and/or precipitation in aqueous phase. The process for producing these red iron oxide pigments is complex and necessitates continual monitoring of the isoelectric point. The process is extended to other iron oxide color pigments in DE 36 32 913 A1. The dlsadvanges of the prosess, however, remains the same.
EP 0 634 991 A1 describes surface-modified particles and also a process for producing them. The particles disclosed therein are similar to those from EP 0 199 975 A1. They differ only in a second coating with at least one dispersion promoter. Examples given of such promoters include ligninsulphonates and polyacrylates. The production of particles of this kind is always a multi-stage operation and is therefore extensive.
U.S. Pat. No. 6,758,893 B2 describes a process of producing extrusion granulates. In the sole example, iron oxide yellow pigments are used to colour a cement system. Although the problem the patent sought to solve was to produce rapidly dispersible granules, the cement coloured with iron oxide yellow granules is yellower but also considerably less colour strength. From the published ΔL* values it can be concluded that the extrusion granules have approximately 10% to 15% less colour strength then the starting iron oxide yellow powder. The disclosed extrusion process therefore only delivers granules with less colour strength.
U.S. Pat. No. 5,853,476 A1 and/or EP 1 027 302 B1 describe a process to colour a cement system with compacted inorganic pigment granules, whereby the colouring effect of the compacted inorganic granules in the cement system exceeds that of the powder standard. Although the colourimity of the cement system is described in two examples, whereby the colorizing effect of the inorganic compacted pigment granules and the powder standard is documented with the help of a colour measuring system, no data on the colour values and colour strength is disclosed. Both disclosed examples merely describe the visual colour-matching of the testing specimens manufactured. The testing specimens coloured with the compacted inorganic pigment granules are described as “redder and lighter” in comparison to the powder standard in the case of a compacted iron oxide red granule and as “yellower and lighter” in comparison to an iron oxide yellow granule. These pigment granules have by their own account less colour strength then the original powder (“lighter”). A disadvantage of the described manufacturing process for the compacted inorganic pigment granules is also the relative high proportion of a dispersing agent of over 3 wt-% based on pigment, which at the same time also acts as a binder. Lignin sulphate is preferably used as a dispersing agent. This acts as a liquefier in concrete mixtures, affects the water-cement-relationship and affects the concrete consistency.